1. Field of the Invention
This invention relates to an optical pickup for recording on and reproducing from recording media of different recording densities, such as a high-density optical disk, a compact disk and the like.
2. Description of the Related Art
A conventional optical pickup for recording and reproducing on/from a high-density recording optical disk and a compact disk will be described. For convenience, an explanation will be given with a DVD (digital video disk) as a high-density optical disk, and a CD (compact disk) as a low-density optical disk.
FIG. 13 shows a plan view of a conventional optical pickup, and a cross-sectional view of an essential part thereof. In FIG. 13, the reference numeral 50 denotes an optical pickup for a high-density optical disk, and a high-density optical disk objective lens 54 for condensing a laser beam 53 onto the high-density optical disk 52 is adhesively bonded and fixed to an objective lens holding tube 51. A coil unit 55, comprising a focusing coil and a tracking coil adapted for actuation in a focusing direction and a tracking direction, is adhesively bonded and fixed to the objective lens holding tube 51. The coil unit 55 is fitted in a permanent magnet to form a magnetic circuit for driving the objective lens holding tube 51 in the focusing direction and the tracking direction. The objective lens holding tube 51 is held in a neutral position by a non-magnetic, electrically conductive, linear elastic member 57 and electric power is supplied to the coil unit 55.
An optical system of the optical pickup 50 of the above construction for reproduction from the high-density optical disk will now be described. An optical unit 61 for a high-density optical disk contains a light-emitting element and a light-receiving element for a laser beam 53 having a wavelength of 635 to 650 nm. The laser beam 53 passes through a collimator lens 62 to be converted to parallel rays of light, which then are totally reflected by a surface of a rise mirror 63 with a multi-layer coating to be condensed by the high-density optical disk objective lens 54, and form an optical spot on the high-density optical disk 52.
Then, the laser beam 53 reflected by the high-density optical disk 52 goes back along the above path, and is again incident on the high-density optical disk optical unit 61 to pass through a diffraction grating (not shown) to be received by the light-receiving element (not shown). In accordance with optical information, which is subjected to photoelectric conversion by the light-receiving element, focus detection is effected by a conventional optical Foucault method, and track detection is effected by a conventional phase difference method. Thus, the high-density optical disk objective lens 54 is always focused on the high-density optical disk 52, and is controlled to follow the information track. The high-density optical disk (DVD) 52 is driven by a spindle motor 71 for rotation.
Next, the low-density optical disk (CD) will be described. The reference numeral 70 denotes the optical pickup for a low-density optical disk, and the construction and operation of the optical pickup 70 are similar to those of the optical pickup 50 for a high-density optical disk, and therefore explanation thereof will be omitted. In its optical system, an optical unit 64 for a low-density optical disk contains a light-emitting element and a light-receiving element for a laser beam 65 having a wavelength of 780 nm. Laser beam 65 is totally reflected by a surface of a rise mirror 66 with a multi-layer coating to be condensed by a low-density optical disk objective lens 67 to form an optical spot on the low-density optical disk 68.
Then, the laser beam 65 reflected by the low-density optical disk 68 goes back along the above path to be again incident on the low-density optical disk optical unit 64 to pass through a diffraction grating (not shown) to be received by the light-receiving element (not shown). In accordance with optical information, which is subjected to photoelectric conversion by the light-receiving element, focus detection is effected by a conventional optical Foucault method, and track detection is effected by a conventional three-beam method. Thus, the low-density optical disk objective lens 67 is always focused on the low-density optical disk 68, and is controlled to follow the information track.
Thus, the high-density optical disk optical pickup 50 and the low-density optical disk optical pickup 70 are constructed independently of each other whereby recording and reproduction can be effected for the compact disk.
However, the above conventional optical pickup construction includes the two independent optical systems having the high-density optical disk optical pickup and the optical pickup for reproduction from the compact disk, and therefore involves problems that the number of the component parts is large, it is difficult to achieve a compact design of the optical pickup unit, and that it is difficult to reduce consumption of electric power and cost.